#include <bits/stdc++.h>
#include <bits/stdc++.h>
#include <bits/stdc++.h>
using namespace std;
// #include <atcoder/modint>
// using namespace atcoder;
// using mint = modint998244353;
using ll = long long;
#define fix(x) fixed << setprecision(x)
#define rep(i, n) for(int i = 0; i < n; ++i)
#define all(x) (x).begin(),(x).end()
template<class T>bool chmin(T&a, const T&b){if(a>b){a=b;return 1;}return 0;}
template<class T>bool chmax(T&a, const T&b){if(a<b){a=b;return 1;}return 0;}
constexpr ll INFLL = (1LL << 62), MOD = 998244353;
constexpr int INF = (1 << 30);

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    string s;
    cin >> s;
    reverse(all(s));
    int l = -1, n = s.size();
    ll ans = 0;
    rep(i,n-2){
        if(s.substr(i,3)=="011"){
            ans += i-l;
            s[i+1] = s[i+2] = '0';
            l += 2;
        }
        if(s[i]=='1') ++l;
    }
    cout << ans << '\n';
    return 0;
}